1. Field of the Invention
This invention relates to vehicular semi-automatic mechanical transmission systems and, in particular, to semi-automatic mechanical transmission systems of the type providing partially automatic implementation of preselected shifting of mechanical transmission gear ratios. Preferably, such systems have at least one mode of operation wherein the shifting of ratio changes are automatically preselected by the system central processing unit.
In particular, the invention relates to semi-automatic transmission systems having at least partially automatic shift implementation wherein the vehicle operator is required to manipulate the throttle to cause substantially synchronous conditions for allowing an actuator to implement engagement of a selected or target gear ratio.
More particularly, a control system/method for transmission systems of the type described wherein, under certain conditions, such as an accelerating vehicle, the transmission will be reengaged from a neutral condition after a preselected period of time regardless of the operator's inability to achieve substantially synchronous conditions for engagement of a selected gear ratio.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
While such semi-automatic mechanical transmission systems are very well received as they are somewhat less expensive than fully automatic transmission systems, allow manual clutch control for low speed operation and/or do not require automatic selection of the operating gear ratio, they may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained.
Many of the drawbacks of the prior art are overcome or minimized by the provision of a semi-automatic shift implementation system/method for a mechanical transmission system for use in vehicles having a manually only controlled engine throttle means, and a manually only controlled master clutch. The system preferably has at least one mode of operation wherein the shifts to be semi-automatically implemented are automatically preselected and includes a control/display panel or console for operator selection of operation in the automatic preselection mode and indication of automatic preselection of upshifts, downshifts or shifts into neutral.
The control/display device will display the selected but not yet implemented shift as well as the current status of the transmission, and, preferably will also allow the operator to manually select/preselect a shift into a higher ratio, a lower ratio or into neutral. Preferably, the control device will also allow a manually or an automatically preselected shift to be cancelled.
Transmission systems of this type may be seen by reference to U.S. Pat. No. 4,991,099, the disclosure of which is incorporated herein by reference.
As such systems rely upon manual throttle manipulation by the vehicle operator to cause substantially synchronous conditions for shifting from neutral into a selected ratio, inattention or lack of skill may result in the transmission remaining in neutral for a prolonged period of time. Such a condition is not desirable, especially if a heavy vehicle is descending a steep grade and engine braking is desired and/or required.
This situation is addressed in above-mentioned, allowed copending applications Ser. Nos. 368,492 and 383,686, respectively, wherein the requirements for sensing substantially synchronous conditions are eased with the passage of time and shifts from a currently engaged ratio into neutral in preparation for shifting into a selected ratio are prohibited under certain conditions, respectively. The disclosures of allowed, copending applications Ser. Nos. 368,492 and 383,686 are incorporated herein by reference.